Detecting ultra-high energy cosmic rays from space with unprecedented acceptance: objectives and design of the JEM-EUSO mission

The Extreme Universe Space Observatory on the Japanese Experiment Module (JEM-EUSO) of the Interna- tional Space Station (ISS) is the first mission that will study from space Ultra High-Energy Cosmic Rays (UHECR). JEM-EUSO will observe Extensive Air Showers (EAS) pro- duced by UHECRs traversing the Earth's atmosphere from above. For each event, the detector will make accurate mea- surements of the energy, arrival direction and nature of the primary particle using a target volume far greater than what is achievable from ground. The corresponding increase in statistics will help to clarify the origin and sources of UHE- CRs as well as the environment traversed during production and propagation. Possibly this will bring new light onto par- ticle physics mechanisms operating at energies well beyond those achievable by man-made accelerators. The spectrum of scientific goals of the JEM-EUSO mission includes as ex- ploratory objectives the detection of high-energy gamma ray

Vertical fine structure and time evolution of plasma irregularities in the E s layer observed by a high-resolution Ca+ lidar

Abstract The vertical fine structures and the time evolution of plasma irregularities in the sporadic E (E s) layer were observed via calcium ion (Ca+) density measurements using a resonance scattering lidar with a high time-height resolution (5 s and 15 m) at Tachikawa (35.7°N, 139.4°E) on December 24, 2014. The observation successfully provided clearer fine structures of plasma irregularities, such as quasi-sinusoidal height variation, localized clumps, “cats-eye” structures, and twist structures, in the sporadic Ca+ ($${{\text{Ca}}^{+}}_{\text{s}}$$ Ca+s ) layers at around 100 km altitude. These fine structures suggested that the Kelvin–Helmholtz instabilities occurred in the neutral atmosphere whose density changed temporarily or spatially. The maximum Ca+ density in the $${{\text{Ca}}^{+}}_{\text{s}}$$ Ca+s layer was two orders of magnitude smaller than the maximum electron density estimated from the critical frequency (f o E s) simultaneously observed by the ionosonde at Kokubunji (35.7°N, 139.5°E). A strong positive correlation with a coefficient of 0.91 suggests that Ca+ contributes forming the E s layer as well as major metallic ions Fe+ and Mg+ in the lower thermosphere. Moreover, the formation of a new $${{\text{Ca}}^{+}}_{\text{s}}$$ Ca+s layer at 110 km and the upward motions of the $${{\text{Ca}}^{+}}_{\text{s}}$$ Ca+s layers at 100 km and 110 km were observed before the local sunrise and just after the sunrise time at the conjugation point. Although the presence or absence of a causal relationship with the sunrise time was not clear, a possible explanation for the formation and the upward motions of the $${{\text{Ca}}^{+}}_{\text{s}}$$ Ca+s layers was the occurrence of strong horizontal wind, rather than the enhancement of the eastward electric field